This disclosure relates to aircraft safety, and more specifically to a temperature controlled nitrogen generation system.
Aircraft fuel tanks and containers can contain potentially combustible combinations of oxygen, fuel vapors, and ignition sources. In order to prevent combustion, the ullage of fuel tanks and containers is filled with air with high nitrogen concentration, or nitrogen-enriched air (NEA), such that the oxygen concentration in the ullage is less than 12%. A membrane-based nitrogen generation system (NGS) is commonly used to produce NEA for inerting fuel tanks and containers. A membrane-based NGS has an air separation module with a polymeric membrane which separates air into NEA and oxygen-enriched air (OEA). However, at a given temperature, a polymeric membrane material has a fixed permeability (defined as the transport flux of a gas through the membrane per unit driving force, i.e. partial pressure difference between the two sides of the membrane per unit membrane thickness) and selectivity (selectivity αAB is defined as the ratio of permeability of one gas component A to the permeability of another gas component B in a gas mixture), which limits the performance of the air separation module. As a result, a larger and heavier NGS than desired is required to provide adequate fuel tank and container inerting throughout the flight profile of an aircraft.